Ligaments are tough bands of tissue which serve to connect the articular extremities of bones, or to support or retain organs in place within the body. Ligaments are typically composed of coarse bundles of dense white fibrous tissue which are disposed in a parallel or closely interlaced manner, with the fibrous tissue being pliant and flexible, but not extensible.
In many cases, ligaments are torn or ruptured as a result of accidents. As a result, various procedures have been developed to repair or replace such damaged ligaments.
For example, in the human knee, the anterior and posterior cruciate ligaments (i.e., the ACL and PCL) extend between the top end of the tibia and the bottom end of the femur. The ACL and PCL cooperate, together with other ligaments and soft tissue, to provide both static and dynamic stability to the knee. Often, the anterior cruciate ligament (i.e., the ACL) is ruptured or torn as a result of, for example, a sports-related injury. Consequently, various surgical procedures have been developed for reconstructing the ACL so as to restore normal function to the knee.
In many instances, the ACL may be reconstructed by replacing the ruptured ACL with a synthetic or harvested graft ligament. More particularly, with such procedures, bone tunnels are typically formed in the top end of the tibia and the bottom end of the femur, with one end of the graft ligament being positioned in the femoral tunnel and the other end of the graft ligament being positioned in the tibial tunnel. The two ends of the graft ligament are anchored in place in various ways well known in the art so that the graft ligament extends between the femur and the tibia in substantially the same way, and with substantially the same function, as the original ACL. This graft ligament then cooperates with the surrounding anatomical structures so as to restore normal function to the knee.
It will, of course, be appreciated that a complex interdependency exists between the ACL and the other elements of the knee, e.g., the bones, the other knee ligaments, and other soft tissue. Consequently, it is critical that the graft ACL be disposed in exactly the right position relative to the other anatomical structures of the knee if normal knee function is to be restored. Correspondingly, it has been found that the aforementioned bone tunnels must be precisely positioned in the tibia and femur if successful reconstruction of the ACL is to be achieved. Unfortunately, proper positioning of these bone tunnels to satisfy isometric considerations can sometimes lead to anatomical conflicts within the knee when the graft ACL is installed within the knee.
More particularly, the ACL normally extends between the bottom end of the femur and the top end of the tibia, with the body of the ACL passing through the femur's intercondylar notch and across the interior of the knee joint. See, for example, FIGS. 1 and 2, which show a natural ACL 5 extending between the bottom end of a femur 10 and the top end of a tibia 15, with the body of ACL 5 passing through the femur's intercondylar notch 20. Also shown is a natural PCL 25 extending between the bottom end of femur 10 and the top end of tibia 15.
It is to be appreciated that the position of the various knee elements move relative to one another as the knee is flexed through a range of natural motions. See, for example, FIG. 3, which shows ACL 5 moving across a 40.degree. arc as the knee joint is flexed through a 140.degree. motion.
Due to the complex geometries of the knee, where a damaged ACL is to be replaced by a graft ACL, it is critical that the graft ACL be connected at precisely the right locations on the bottom end of the femur and top end of the tibia. Thus, and looking now at FIGS. 4 and 5, where a damaged ACL is to be replaced by a graft ACL, the damaged ACL is first cleared away and then bone tunnels 30 and 35 are formed in the tibia and femur, respectively. The precise locations of these bone tunnels 30 and 35 are dictated by the isometric relationships of the knee. In practice, bone tunnels 30 and 35 are formed using a surgical drill guide which is keyed to certain parts of the patient's anatomy, e.g., to the patient's tibial plateau. Once bone tunnels 30 and 35 have been formed, the graft ACL may be installed in ways well known in the art. See, for example, FIGS. 6 and 7, which show a graft ACL 5A having one end mounted to femur 10 and the other end mounted to tibia 15.
Unfortunately, in some situations, proper isometric placement of bone tunnels 30 and 35 may cause anatomical conflicts within the knee when the graft ACL is installed in the patient. By way of example, and of particular interest in connection with the present invention, proper isometric placement of bone tunnels 30 and 35 may result in portions of the femur impinging upon the graft ACL as the knee is moved through its full range of natural motions. See, for example, FIG. 8, which shows one of the femur's condyles 40 impinging upon a graft ACL 5A extending through the femur's intercondylar notch 20; and FIG. 9, which shows the roof the femur's intercondylar notch impinging on the graft ACL 5A in the vicinity of arrow 42.
Impingement can occur for a variety of reasons. For one thing, the intercondylar notch of many patients (particularly those who are susceptible to rupture of the ACL) is frequently small to begin with. For another thing, the graft ACL (i.e., the synthetic or harvested graft ligament which is being installed in place of the damaged natural ACL) is generally fairly large.
Additionally, slight mispositioning of bone tunnels 30 and 35 can also lead to impingement problems.
Unfortunately, impingement of the femur on the graft ligament can reduce the effectiveness of the ACL reconstruction procedure or even cause it to fail altogether.
Thus, when performing an ACL reconstruction procedure, the surgeon generally tries to ensure that there is sufficient room within the patient's intercondylar notch to receive the graft ligament. This is generally done by performing notchplasty, i.e., by surgically removing any impinging bone from the sides and/or roof of the intercondylar notch. At the same time, of course, it is also important that the surgeon remove no more bone than is absolutely necessary, so as to minimize trauma to the patient.
Unfortunately, it is difficult for the surgeon to accurately gauge the precise amount of bone that must be removed from the notch in order to avoid impingement. For one thing, the ACL reconstruction procedure is typically performed arthroscopically, so that the surgeon's view of the surgical site is frequently fairly restricted. For another thing, the surgeon typically will not know the precise space that the graft ACL will occupy until the graft is actually in place; but at that point in the procedure, it is frequently difficult to insert additional bone-cutting instruments into the joint so as to remove more bone, particularly without cutting the graft ACL. Furthermore, experience has shown that the most serious problems with impingement occur superiorly; but even with the graft ligament in place, the surgeon is generally unable to see impingement at this location due to limitations in arthroscopic visualization. Also, the surgeon typically performs the ACL reconstruction procedure in a relatively static context, i.e., with the knee being relatively stationary at any given moment during the reconstruction procedure. However, the knee must perform (and impingement must be avoided) in a relatively dynamic context, i.e., as the knee is moved throughout a full range of natural motions. This complicates the surgeon's task of eliminating impingement.